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How to tell if a cameo is authentic 
Know which materials are most authentic. 
Authentic carved cameos can be made of shell or natural stone, while authentic painted cameos are typically made from porcelain. 
As a general rule, any carved cameo made from a natural material can be considered authentic.
Some of the materials used include shell, agate, carnelian, onyx, ivory, lava, coral, jet, bone, mother of pearl, and various gemstones. A cameo is referred to as being non-authentic or fake if it has been made with plastic or resin.